Moon and Mars

The crescent Moon and the planet Mars are quite low in the western sky as twilight fades away, and set not long after the sky gets good and dark. Mars looks like a moderately bright orange star to the upper left of the Moon.

The Moon probably formed after another planet slammed into the young Earth, spewing debris into space. Much of that material coalesced to form the Moon — and perhaps several moons; the others fell back to Earth or merged with the one moon we have today.

The same process may also have given birth to the moons of Mars. Phobos and Deimos are lumpy boulders only a few miles across. That led to speculation that they are asteroids that were somehow captured when they wandered close to Mars.

Catching an asteroid is a tricky process, though, so many scientists questioned that scenario. And today, the “capture” idea has given way to a different model: that Phobos and Deimos formed from the debris from an impact between Mars and a smaller body. The case isn’t closed, though — scientists continue to debate the origins of these tiny moons.

But their fates are clear. Deimos is slowly inching away from Mars. Phobos, on the other hand, is inching toward Mars — by about an inch a year, in fact. Eventually, it’ll either slam into Mars or be pulverized before it hits, forming a ring around the planet — a ring similar to the one that may have given birth to the tiny moon.

More about the moons of Mars tomorrow.

Script by Damond Benningfield

For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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